A recent strong demand for high density and highly integrated LSIs (large-scale integrated circuits) radically accelerates miniaturization of wiring patterns.
A method of using short wavelength radiation in lithography is one of the means for responding to the progress in miniaturization. In recent years, deep ultraviolet rays such as an F2 excimer laser (wavelength: 157 nm), ArF excimer laser (wavelength: 193 nm), or KrF excimer laser (wavelength: 248 nm), electron beams, or X rays are used instead of ultraviolet rays such as g-line (wavelength: 436 nm) and i-line (wavelength: 365 nm). Deep ultraviolet rays with a wavelength of 193 nm or less are attracting particular attention.
As a resist applicable to such short wavelength radiations, a number of resists utilizing a chemical amplification effect between a component having an acid-dissociable functional group and a photoacid generator which generates an acid upon irradiation (hereinafter called “exposure”) has been proposed. Such a resist is hereinafter called a chemically amplified resist.
As a radiation sensitive resin composition applicable to short wavelength radiations, a number of compositions utilizing a chemical amplification effect between a component having an acid-dissociable functional group and a photoacid generator which generates an acid upon irradiation (hereinafter called “exposure”) has been proposed. Such a composition is hereinafter called a chemically-amplified radiation sensitive composition.
As the chemically-amplified radiation sensitive composition, Japanese Patent Publication No. 27660/1990 discloses a composition comprising a polymer containing a t-butyl ester group of carboxylic acid or a t-butylcarbonate group of phenol and a photoacid generator. This composition utilizes the effect of the polymer to release a t-butyl ester group or t-butyl carbonate group by the action of an acid generated upon exposure to form an acidic group such as a carboxylic group or a phenolic hydroxyl group, which renders an exposed area on a resist film readily soluble in an alkaline developer.
Novolac resins, poly(vinylphenol) resins, and the like have been conventionally used in resist compositions. However, because these resins exhibit strong absorbance at a wavelength of 193 nm due to inclusion of aromatic rings in the structure, a lithographic process by an ArF excimer laser, for example, using these resins cannot provide high accuracy corresponding to high photosensitivity, high resolution, and a high aspect ratio.
Therefore, a resin for use in a resist, transparent to a wavelength of 193 nm or less, particularly to an F2 excimer laser (wavelength: 157 nm), Kr2 excimer laser (wavelength: 147 nm), or ArKr excimer laser (wavelength: 134 nm) and exhibiting excellent dry etching resistance equivalent to or better than aromatic rings has been desired. A polysiloxane is one such a polymer. R. R. Kunz et al. of the MIT have reported their research results showing excellent transparency of a polysiloxane at a wavelength of 193 nm or less, particularly at 157 nm, commenting on superiority of this polymer as a resist in a lithographic process using radiation with a wavelength of 193 nm or less (J. Photopolym. Sci. Technol., Vol. 12, No. 4, 1999). Moreover, polysiloxanes are known to exhibit excellent dry etching properties. In particular, a resist containing polyorganosilsesquioxane having a ladder structure is known to possess high plasma resistance.
Several resist materials using a siloxane polymer have also been reported. For example, Japanese Patent Application Laid-open No. 323611/1993 discloses a chemically amplified radiation sensitive composition comprising a polysiloxane having an acid-dissociable group such as a carboxylic acid ester group, phenol ether group, etc., on the side chain, bonded to a silicon atom via one or more carbon atoms. However, this polysiloxane cannot provide high resolution if the acid-dissociable carboxylic acid groups on the side chain do not efficiently dissociate. If a large number of acid-dissociable groups dissociate, on the other hand, the curing shrinkage stress of the resist film increases, causing cracks and peels in the resist film.
Japanese Patent Application Laid-open No. 160623/1996 discloses a positive tone resist using a polymer in which the carboxyl group of poly(2-carboxyethylsiloxane) is protected with an acid-dissociable group such as a t-butyl group. Since this resist protects the carboxyl groups only insufficiently, it is difficult to develop the resist containing a large amount of carboxylic acid components remaining in the non-exposed area using a common alkaline developing solution.
Japanese Patent Application Laid-open No. 60733/1999 discloses a chemically amplified radiation sensitive composition containing a polyorganosilsesquioxane having an acid-dissociable ester group. This polyorganosilsesquioxane is prepared by the addition reaction of an acid-dissociable group-containing (meth)acryl monomer to a condensation product of vinyl trialkoxysilane, γ-methacryloxypropyltrialkoxysilane, or the like. The resin has a problem of insufficient transparency to light with a wavelength of 193 nm or less due to unsaturated groups originating from a (meth)acrylic monomer remaining on the polymer side chains. The patent specification also describes a resist resin composition containing a polymer made by the esterification of polyhydroxycarbonylethylsilsesquioxane with t-butyl alcohol. This polymer also has the same problem as a resist as encountered by the polymer disclosed in Japanese Patent Application Laid-open No. 160623/1996 due to a low degree of carboxyl group protection.
In addition, to respond to miniaturization in recent years, the chemically amplified radiation sensitive composition must not only exhibit higher resolution, but also be applicable to substrates with different reflection coefficients. In particular, when applied to a substrate with a large reflection coefficient, effects of standing waves and swing curves must be minimized. To this end, it is essential to control radiation transmittance. One method of reducing radiation transmittance is increasing the amount of a photoacid generator with a low radiation transmittance. However, this method is not necessarily appropriate in view of resist performance. The addition of a third component, such as a dye, is considered to be more appropriate.
Japanese Patent Application Laid-open Publications No. 319155/1995 and No. 265061/1999 propose the addition of an anthracene compound as a dye to control the radiation transmittance of chemically amplified radiation sensitive compositions. However, merely adding a compound with a low radiation transmittance may impair performance as a resist, such as decreased resolution and incomplete development. In addition, since anthracene compounds are generally sublimative, the exposure apparatus may be adversely affected. Moreover, many anthracene compounds exhibit insufficient compatibility with resin components and additives contained in chemically amplified radiation sensitive compositions.
Japanese Patent Application Laid-open Publication No. 120628/1998 discloses a carboxylic acid derivative having a tricyclic aromatic skeleton, such as an anthracene skeleton, with a carboxyl group bonded via a divalent hydrocarbon group or an oxygen atom, the carboxyl group being protected with a group unstable in the presence of an acid. The patent application describes that the carboxylic acid derivative exhibits superior light absorption properties and is suitable as an additive to chemically amplified radiation sensitive compositions.
Under the above-described technological background and in view of further technological development in the photolithographic process requiring increasingly stringent performance accommodating the rapid progress of miniaturization, development of a chemically amplified radiation sensitive composition exhibiting high transparency to radiation with a wavelength of 193 nm or less and possessing excellent basic properties as a resist still remains as an important technological subject.